1. Field of the Invention
The present invention relates to systems and methods for rapid charging of a rechargeable battery in a manner that the rapid charging is automatically terminated in response to a monitored battery parameter reaching or passing a target or limit value in order to mitigate overcharging.
2. Description of the Related Art
Portable devices of various types are powered by one or more rechargeable batteries which require rapid recharging to a substantially fully charged state in order that the device is readily available for use. Examples of such battery powered devices are cordless and cellular phone handsets, shavers, and computers. In order to trigger automatic termination of rapid recharging of the battery when a substantially fully charged state is reached, it is known that the battery charger control include means for monitoring the rate of increase over time or increase between successive samples of the battery temperature and for determining when the rate of increase first equals or exceeds a predetermined target or threshold rate. Unfortunately, the inventors herein have determined with respect to a Nickel Cadmium (NiCad) battery in particular, that the battery temperature will not exhibit a significant and reliably detectable rate or amount of increase until it is too late to terminate the rapid charging without causing permanent damage due to overcharging after multiple discharge/recharge cycles.
It is also possible to monitor the rate of change or change between samples of the battery voltage and to instead determine when the rate of change equals or falls below a predetermined target or threshold rate. However, as in the case of detection of the rate of change of battery temperature, battery damage will occur due to overcharging after multiple rechargings if each rapid charging is not terminated until the time the rate of change battery voltage falls below a predetermined reliably detectable threshold value.